Antirollback mechanism

ABSTRACT

A loader unit mounted on a tractor and including pivotally mounted lift arms on which there is pivotally supported a bucket controlled by a hydraulic circuit including a bucket control cylinder. The loader unit includes an antirollback mechanism incorporating a control member and a control link. The control member is moved relative to the link in response to movement of the bucket control operating lever; and the control link is movable relative to the control member by raising and lowering of the lift arms and pivoting of the bucket relative to the lift arms so that the link engages the control member to prevent rollback of the bucket when the bucket and the arms are in position to permit rearward dumping of the bucket.

United States Patent [72] Inventors Gary L. Beiley [56] References Cited Terre Haute, lnd.; UNITED STATES PATENTS Dickma"! Milwaukee 3 402 84 9 1968 m 214 7 4 pp 790,050 ,I 0 I Go 6 22 Filed Jam 9, 19 9 Primary Examiner-Albert J. Makay 45 patented M 9, 1971 Attorney-Dressler, Goldsmith, Clement & Gordon [73] Assignee J. 1. Case Company v Racme ABSTRACT: A loader unit mounted on a tractor and including pivotally mounted lift arms on which there is pivotally sup ported a bucket controlled by a hydraulic circuit including'a bucket control cylinder. The loader unit includes an antirollback mechanism incorporating a control member and a control link. The control member is moved relative to the link in [54] 'F g K MIECHANISM response to movement of the bucket control operating lever; arms, rawlng 138- and the control link is movable relative to the control member [52] U.S.Cl 214/764, by raising and lowering of the lift arms and pivoting of the 214/776 bucket relative to the lift arms so that the link engages the [5 1] Int. Cl E02f3/30 control member to prevent rollback of the bucket when the [50] Field of Search bucket and the arms are in position to permit rearward dump- 214/764, 763, 762, 775, 776, 773, 771 ing ofthe bucket.

ANTl-RQLLBACK MECHANISM BACKGROUND OF THE INVENTION Material-handling devices such as loaders mounted upon and controlled by various vehicles, are well known. Such loaders include lift arms pivotally mounted to the vehicle which lift arms carry a pivotally mounted bucket at their free end. Typically, at least one hydraulic lift cylinder is connected between the vehicle or a support thereon and the lift arms to raise and lower the lift arms. At least one bucket hydraulic cylinder is connected between the lift arms and the bucket to position the bucket relative to the lift arms.

A slave cylinder is usually provided to modify the action of the bucket cylinder under the control of the raising and lowering movement of the lift arms in order to maintain the bucket at a substantially level position. A typical self-leveling arrange ment of this type is disclosed in Long US. Pat. No. 3,220,580.

, Such material-handling devices and systems operate satisfactorily for their designed purposes. However such arrangements may be deficient because of a failure to prevent rearward dumping of the bucket.

When the lift arms are raised, such rearward dumping of the buckets may present a substantial danger to the operator of the material-handling device. Thus, there is a requirement and. a serious need for some simple device which can be incorporated into material-handling devices to introduce the desired safety factor and prevent the possibility that the bucket might inadvertently be actuated in fashion to cause rearward dumping of the bucket when the lift arms are raised.

SUMMARY OF THE INVENTION The present invention is directed to a positive, mechanical, bucket antirollback mechanism for use in material-handling devices, particularly those of the heavy duty type. The antirollback mechanism is designed to limit operation of the bucket operating lever to prevent rollback of the bucket past its level position when the lift arms are raised above a selected height.

It can be appreciated that as the lift arms are raised, the position of the bucket relative to the lift-arm changes while the bucket remains level or at any fixed position relative to the ground. Thus, any antirollback device to be effective must take into account these varying relationships between the bucket and the lift arms and be capable of preventing rollback of the bucket past its level position at any raised position of the lift arm.

At the same time, it is sometimes desirable to roll the bucket back past its level position when the lift arms are lowered into digging or dozing position. When the lift arms are so lowered, there is no danger of dumping the load onto the operator and rollback beyond level position is of assistance in breaking out the bucket as its digs into a load.

In accordance with the present invention there is provided a mechanical antirollback mechanism which prevents rearward tilting of the bucket past its level position when the lift arms are raised, but which permits the desired rollback of the bucket when the lift arms are in their lowered position. In accordance with the present invention there is provided a rigid antirollback link in the form of a rod of fixed length one end of which is pivotally connected to the bucket control linkage interconnecting the bucket, the lift arms and the bucket control cylinders. This bucket control link is slideably supported in a sleeve the end of which remote from the bucket control linkage is pivotally supported adjacent to the pivot point of the lift arms. The free end of the rod extends beyond the end of the lift arms. This control member is mechanically connected to the bucket operating lever. and theposition of the control member is governed by the position of the bucket operating lever.

Thus, the control member is moved towards the free end of the control rod as the operating lever is moved to its first or bucket rollback operating position while the control lever is pivoted away from the free end of the control rod when the operating lever is moved into its second or bucket dump operating position. The movements of the rod and control member relative to each other are such thatthe end of the rod is moved towards the control member as the lift arms are raised and moved away from the control member as the lift arms are lowered. In addition the control rod is moved towards the control member as the bucket is rolled back and is moved away from the control member as the bucket is moved forward into the dump position.

Thus, in operation, as the lift arms are raised, the rod is moved towards the control member. The rod engages the arcuate control surface of the control member as the bucket approaches its level position to prevent further rollback of the bucket past its level position.

Additionally, if the operating lever is moved into its bucket rollback operating position, the control member is moved towards the rod if the bucket is not already at its level position. If the bucket is level, the control member immediately engages the free end of the rod to prevent further movement of the control member towards the rod. In fact, engagement of the rod with the control member forces the control member away from the rod and, therefore, the operating lever out of its sleeve and travels in an arcuate path as the lift arms are raised bucket rollback position into a neutral position.

Thus, it is clear that the relative position and movements of the control member and antirollback control rod are such as to prevent inadvertent, erroneous operation of the operating lever to roll back the bucket past its level position when the lift arms are raised. Simultaneously, this antirollback mechanism supplements the hydraulic self-leveling control to prevent bucket rollback past the level position as the lift arms are raised.

Numerous other advantages and features of the present invention will become readily apparent from the following detailed description of the invention and of one embodiment thereof, from the claims and from the accompanying drawings in which each and every detail shown is fully and completely disclosed as a part of this specification in which like numerals refer to like parts.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of the material-handling device, showing in solid lines the bucket and lift arms in the digging or lowered position and in dotted lines the lift arms in the raised position with the bucket in the level and dump positions;

FIG. 2 is an enlarged side view showing in more detail the antirollback mechanism in various positions of the bucket and lift arm;

FIG. 3 is a plan view partially in section, taken along lines 3-3 of FIG. 2;

FIG. 4 is a partial enlarged side view showing the control member and its donnetion to the operation lever; and

FIG. 5 is an enlarged side view of the control member showing the relationship of its control surface to the path followed by the free end of the antirollback rod.

DETAILED DESCRIPTION Referring now to the drawings, there is shown a materialhandling device 10 including a loader mechanism 12 mounted on the front end of a tractor M. The loader mechanism includes a main frame 16 thatis attached to the tractor by any suitable means. The main frame serves as the main support member for the loader mechanism and includes a pair of uprights l3 (only one being shown) on opposite sides of the tractor. The uprights 18 are connected. at their upper ends by a pivot shaft 20. Although only one side of the loader mechanism 12 is shown, it should be understood that the various components are normally present on both sides of the tractor 14.

The loader mechanism 12 consists of a pair of lift arms 22 pivotally connected to the upper end of the uprights 18 by the pivot shaft 20. A bucket 24 is pivotally connected to the forward end of the lift arms 22.

Each lift arm 22 is pivoted about the pivot shaft by operation of a hydraulic cylinder 26 through the extension or retraction of a piston rod 28 extending outwardly from the cylinder 26. The lower end 30 of each lift arm cylinder 26 is pivotally connected to the lower portion of an upright 18 while the outer end 32 of each lift arm cylinder piston rod 28 is pivotally secured to an intermediate portion of a lift arm 22.

Hydraulic pressure may be applied to either end of the cylinders 26 by operating the lift arm control valve 33. When hydraulic pressure is applied to the piston end of the hydraulic lift arm cylinders 26, the lift arms 22 are raised by pivoting about the pivot shaft 20. Conversely, when pressure is applied to the rod end of the lift arm hydraulic cylinders 26, the lift arms 22 are pivoted in an opposite direction to lower the bucket 24 attached to the end of the arms.

The bucket 24 is pivoted relative to the lift arms 22 by at least one hydraulic bucket cylinder 34. The piston rod 36 of the bucket cylinder 34 is connected to the lift arms 22 near the end thereof while the cylinder 34 itself is coupled to the bucket 24 through a bucket control linkage 38. This bucket linkage is identical for both lift arms and therefore only one such arrangement will be described.

The bucket control linkage 38 includes a forward bucket link 40 one end of which is pivotally secured to the bucket 24 and the opposite end of which is pivotally connected to the end of a rear bucket link 42. The opposite end of the rear bucket link 42 is pivotally connected to an intermediate portion of the lift arms 22. it can thus be seen that pivotal movement of the rear bucket link 42 causes pivotal movement of the bucket24 relative to the lift arms 22. To effectuate movement of the rear bucket link 42, the bucket hydraulic cylinder 34 is pivotally connected thereto intermediate its ends.

Application of hydraulic pressure to the rod end of the bucket cylinder 34 causes the bucket 24 to pivot forwardly relative to the lift arms 22. Conversely, application of hydraulic pressure to the piston end of the bucket cylinder 34 causes the bucket 24 to pivot rearwardly, i.e., to rollback from the dump position through the dig position to the carry or level position. It is, of course, understood that the two bucket control linkages 38 operate simultaneously to bring about the desired results.

It can be appreciated that when the lift arms 22 are raised, the bucket 24, if it remains in a fixed position relative to the arms, would tend to tilt rearwardly. As a result, a load in the bucket 24 would be dumped back onto the tractor and onto the operator, if such were the case. A slave cylinder 44 connected between the lower region of an upright 18 and the rear end of a lift arm 22 provides self-leveling of the bucket 24 as the lift arms 22 are raised. The leveling action of the arrangement is functionally similar to that shown in FIG. 2 of the Long US. Pat. No. 3,220,580.

in the arrangement of Long US. Pat. No. 3,220,580,, control of the hydraulic bucket cylinder 34 may be effected independently of the position of the lift arms 22. As a result the bucket cylinder 34 can be operated fully in either direction at any position of the lift arms 22. In the event of operator error, the bucket 24 could be tilted rearwardly, i.e., rolled back, thereby dumping a load on the vehicle if the lift arms 22 are raised. This can be quite dangerous to the operator particularly when large loads are being handled.

In accordance with the present invention, there is provided a mechanical interlock effective when the lift arms 22 are raised above a selected position to prevent rearward tilting or rollback of the bucket 24 past its level position while permitting forward tilting of the bucket for dumping of the load.

This mechanism includes an antirollback control link 46 having a control rod 48 and a sleeve 50. The rod is pivotally connected to the rear bucket link 42 intermediate the pivotal connections thereof 'to the lift arms 22 and to the bucket cylinder 34. The rod 48 is slideably supported in the sleeve 50. The end 52 of the sleeve 50 closest to the bucket control linkage 38 is free to move along the rod, while the other end 54 of the sleeve 50 terminates short of the free end 56 of the rod 48 in order to eliminate interference with the rod end 56. The sleeve 50 is attached to a bracket 56 which is pivotally mounted to the upright 18 at a point beyond the free end 56 of the rod 48 and adjacent to the pivot shaft 20 about which the lift arms 22 pivot.

This arrangement allows the rod 48 to move rearwardly as the lift arms 22 are raised and as the bucket 24 is rolled back. Conversely, the rod 48 moves forwardly when the bucket 24 is rolled forward and when the lift arms 22 are lowered.

An antirollback conu'ol member 60 is pivotally mounted on the upright 18 and is provided with an arcuate control surface 62 disposed adjacent to the free end 56 of the antirollback rod 43. The antirollback control pivot shaft is connected to a bucket operating lever 64 through a bucket operating linkage 66 which also connects the operating lever 64 to the bucket control valve 68 As a result, when the operating lever 64 is moved into a first position, it operates the bucket control valve 68 to apply hydraulic pressure to the piston end of the bucket control cylinder 34 thereby causing the bucket 24 to roll back. This rollback of the bucket moves the control rod 48 towards the control member 60. Movement of the operating lever 64 into its first position also operates on the antirollback control member 60 through operating linkage 66 to pivot the control member 60 forwardly toward the free end 56 of the antirollback rod 48.

Conversely, when the operating lever 64 is moved into its second or bucket dump position, it operates the bucket control valve 68 to apply hydraulic pressure to the rod end of the bucket control cylinder 34, thereby causing the bucket 24 to pivot forwardly, and causing the rod 48 to move away from the control member 60. Movement of operating lever 64 into its second position also causes the antirollback control member 60 to pivot away from the free end 56 of the antirollback rod 48.

The arcuate control surface 62 of the antirollback control member 60 is selected to coincide with the path followed by the free end 56 of the antirollback control rod 48 when the lift arms 22 are raised with the bucket 24 automatically maintained at its level position. Thus, when the bucket operating lever 64 is in neutral, the free. end 56 of the rod 48 remains closely adjacent to the arcuate control surface 62 of the antirollback control link as the lift arms 22 are raised, as can be seen in FIG. 5.

By reference to FIGS. 4 and 5, it can be appreciated that the relationship of the rod 48 to the control surface of the antirollback control member 60 prevents additional rollback of the bucket 24 past its level position. If an attempt were made to move the operating lever 64 into its first, bucket rollback position, the control member 60 would be rotated towards the free end 56 of the rod 48 (clockwise in FIGS. 4 and 5). The control surface 62 of the control member 60 would engage the end 56 of the rod 48 immediately, thereby preventing movement of the operating lever 64 into the rollback position.

Since the position of the rod 48 varies as a function as a position of the bucket 24 and lift arms 22, rollback of the bucket 24 moves the free end 56 of the rod 48 towards the control surface 62 of the control member 60. Although the antirollback mechanism of the present invention could operate if one or the other of the control member 60 or the rod 43 remained stationary, the combined movement of both the control member 60 and rod 48 is beneficial for a number of reasons.

Thus, for example, when both the control member 60 and the rod 48 move toward each other during bucket rollback it is quite apparent that they will make contact quicker than would be the case if one remained stationary. The movement of both the control member 60 and rod 43. also results in quicker contact between the two since the free end 56 of the rod 48 can be positioned closely adjacent to the control surface 62 of the control member 60 during raising andlowering of the lift arms.

Furthermore, combined action of both the control member 6% and the rod 48 provides additional insurance that the antirollback mechanism will operate properly, since, as explained above, the free end 56 of the rod 48 engages the control surface 62 of the control member 60 as the bucket starts to roll back past its level position. When this occurs, the control member 60 is caused to rotate counterclockwise (FIG. 4) thereby forcing the operating lever 64 out of the rollback position to close the bucket control valve 68 thereby stoppingrollback of the bucket.

This relationship can also be used as an auxiliary self-leveling mechanism should the hydraulic self-leveler fail. Under these circumstances, the free end 56 of the control rod 48 would engage the control surface 62 of the control member 60 as the lift arms are raised without leveling of the bucket. As a result, the control member 60 would be rotated from its neutral position counterclockwise to force the operating lever 64 into its dump position, thereby operating the bucket control valve 68 to pivot the bucket 24 forwardly to keep the bucket at a level position. I

The arrangement of the antirollback control member 60 and rod 48 is such as to permit dumping of the bucket at any position of the.lift arms 22. When the operatinglever 64 is moved into the bucket dump position, the control member 60 is moved away from the free end 56 of the antirollback rod 48 and simultaneously the forward pivoting movement of the bucket 24 pulls the control rod 48 away from the control surface 62 of the antirollback control member 60. g

The control member 60 terminates at a point as can be seen by reference to FIG. 5 which'allows the bucket 24 to be rolled past its level position when the lift arms 22 are below a selected level. As shown in FIG. 5, the bucket may be rolled back past its level position up to a point where the lift arms are about at 10 lift, thus permitting the rollback of the bucket desired for break out of the load.

From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the true spirit and scope of the novel concept of the invention. It is, of course, intended to cover by the appended claims all such modifications as fall within the scope of the claims.

We claim:

It. A material-handling device comprising in combination .a support structure, lift arm means pivotally connected to said support structure, a bucket, means for pivotally supporting said bucket on said lift arm means, means for raising and lowering said lift arm means, a bucket operating system including bucket control linkage connected between said bucket and said lift arm means, a hydraulic circuit comprised of a bucket control cylinder connected between said bucket control linkage and said lift arm means and a bucket control valve, a bucket operating lever, a bucket operating linkage connecting said operating lever, to said bucket control valve for operating said valve and cylinder in response to movement of said bucket operating lever, whereby movement of said bucket operating lever into a first position rolls said bucket back relative to said lift arm means and movement of said bucket operating lever into a second position rolls said bucket forward relative to said lift arm means, a bucket antirollback control member having an arcuate control surface, means for pivotally mounting said bucket antirollback control member on said support structure, a bucket antirollback control rod, means for pivotally connecting one end of said bucket antirollback control rod to said bucket control linkage, a sleeve slideably supporting the other end of said bucket antirollback control rod, means for pivotally mounting said sleeve to said support structure to allow pivoting movement of said other end of said bucket antirollback control rod through the arcuate path defined by the surface of said antirollback control member during raising and lowering of said lift arm means and to allow sliding movement of said bucket antirollback control rod towards said bucket antirollback control member when said lift arm means is raised and said bucket is rolled back and away from said bucket antirollback control member when said lift arm means is lowered and said bucket is rolled forward, and linkage means connecting said bucket antirollback control member to said bucket operating linkage for pivoting said bucket antirollback control member towards said other end of said bucket antirollback control rod in response to movement of said bucket operating lever into its first position and for pivoting said bucket antirollback control member away from said other end in response to movement of said bucket operating lever into its second position, whereby said other end of said bucket antirollback control rod engages the arcuate control surface of said bucket antirollback control member when said bucket is level and said lift arm means is raised to prevent movement of saidbucket operating lever into its first position and rollback of said bucket past its level position.

2. A material-handling device in accordance with claim 1 in which said sleeve terminates short of both ends of said bucket antirollback control rod and said sleeve mounting means includes means for pivotally mounting said sleeve beyond the end thereof whereby the pivoting movement of said bucket antirollback control rod is about a point beyond the end of said sleeve and short of the other end of said bucket antirollback control rod. r i r 3. A material-handling device comprising in combination a support structure, lift arm means, a bucket, means for pivotally supporting said bucket on one end of the said lift arm means, means for connecting said lift arm means to said sup'- port structure, means for operating said bucket to roll said bucket forward and back relative to said lift arm means, a control member, a bucket antirollback link, means for supporting said link between said operating means and said control member for sliding movement of said link towards said control member in response to rollback of said bucket relative to said lift arm means and for sliding movement away from said control member in response to rolling forward of said bucket relative to said lift arm means, said link having a free end facing said control member, means for connecting said control member to said bucket operating means for moving said control member toward said link in response to rollback of said bucket and for moving said control member away from said link in response to rolling forward of bucket relative to said lift arm means, said control member having a surface positioned to be engaged by the free end of said antirollback link when said bucket is at its level position and said operating means is actuated to roll said bucket back relative to said lift arm means, whereby additional movement of said bucket operating means to roll back the bucket past its level position is prevented.

4. A material-handling device in accordance with claim 3 in which said bucket operating means includes an operating lever, movable into a first position to roll back said bucket relative to said lift arm means, in which said means connecting said control member to said bucket operating means includes a mechanical linkage interconnecting said control member and said operating lever for movement of said control member towards said link in response to movement of said operating lever into its first position and for movement of said operating lever out of its first position in response to movement of said control member away from said link, whereby engagement of said link with said control member causes movement thereof away from said link to prevent operation of said lever to roll back said bucket past its level position.

5. A material-handling device in accordance with claim 3 in which said control member includes an arcuate control surface, and in which said link supporting means includes means for allowing pivotal movement of said one end of said link along said arcuate path.

6. A material-handling device in accordance with claim 3 in which said bucket operating means includes bucket control linkage interconnecting said bucket and said lift arm means, and in which the other end of said link is pivotably connected to said bucket linkage.

7. A bucket antirollback mechanism for a material-handling device comprising in combination a support structure, lift arm means, means for pivotally supporting one end of said lift arm means on said support structure, means for raising and lowering said lift arm means, a bucket, means for pivotally supporting said bucket on the other end of said lift arm means, bucket control linkage connected between said bucket and said lift arm means, an operating lever, means connecting said operating lever to said bucket control linkage for operating said linkage to roll said bucket back relative to said lift arm means when said operating lever is in a first position and for rolling said bucket forward relative to said lift arm means when said operating lever is in a second position, an antirollback control member, an antirollback control link, means for connecting one end of said link to said bucket control linkage and for supporting the other end of said link for pivotable and sliding movement of said link towards said control member during rollback of said bucket and away from said control member during forward roll of said bucket, said other end of said link being free and facing said control member, and means for connecting said control member to said operating lever for moving said control member towards said control link during movement of said operating lever into its first position and for moving said control member away from said control link during movement of said operating lever into its second position, said control member having a surface positioned to be engaged by the free end of said control link when said operating lever is in said first position and said raising means has raised said lift arm means beyond a predetermined angle, said con trol member moving away from said link in response to the free end of said link engaging said control member when said operating lever is in its first position and said bucket is rolled back to its level position to move said operating lever out of said first position thereby preventing rollback of said bucket past its level position.

8. A material-handling device comprising in combination lift arm means, a bucket pivotally supported on said lift arm means, means for raising and lowering said lift arm means, means for operating said bucket to roll said bucket forward and back relative to said lift arm means, a control member, a bucket antirollback link, means for supporting one end of said link adjacent to said control member for reciprocable and pivotable movement of said link relative to said control member in response to operation of said bucket and said lift arm means, and means for supporting said control member for movement relative to said one end of said link in response to operation of said bucket operating means whereby engagement of said one end of said link and said control member prevents rollback of said bucket past its level position when said lift arm means is raised in which the reciprocal and pivotable movement of said one end of said link defines an arcuate path, and in which said control member includes an arcuate control surfacedefined by said path.

9. A material-handling device in accordance with claim 8 including bucket control linkage interconnecting said bucket and said lift arm means, and means connecting the other end of said link to said linkage for movement of said one end of said link towards said control member during rollback of said bucket and raising of said lift arm means and for moving said one end of said link away from said control member during forward roll of said bucket and lowering of said lift arm means.

10. A material-handling device in accordance with claim 8 in which said bucket operating means includes a hydraulic cylinder connected between said bucket and said lift arm means and a hydraulic valve for controlling operation of said cylinder to alternatively roll said bucket forward and back, and mechanical linkage means connecting said control member to said valve for moving said control member towards said one end of said link in response to operation of said valve to roll back said bucket and for moving said control member away from said one end of said link in response to operation of said valve to roll said bucket forward, whereby engagement of said link and said control member causes movement of said control member away from said link to close said valve and prevent rollback of the bucket past its level position when said lift arm means are raised. 

1. A material-handling device comprising in combination a support structure, lift arm means pivotally connected to said support structure, a bucket, means for pivotally supporting said bucket on said lift arm means, means for raising and lowering said lift arm means, a bucket operating system including bucket control linkage connected between said bucket and said lift arm means, a hydraulic circuit comprised of a bucket control cylinder connected between said bucket control linkage and said lift arm means and a bucket control valve, a bucket operating lever, a bucket operating linkage connecting said operating lever, to said bucket control valve for operating said valve and cylinder in response to movement of said bucket operating lever, whereby movement of said bucket operating lever into a first position rolls said bucket back relative to said lift arm means and movement of said bucket operating lever into a second position rolls said bucket forward relative to said lift arm means, a bucket antirollback control member having an arcuate control surface, means for pivotally mounting said bucket antirollback control member on said support structure, a bucket antirollback control rod, means for pivotally connecting one end of said bucket antirollback control rod to said bucket control linkage, a sleeve slideably supporting the other end of said bucket antirollback control rod, means for pivotally mounting said sleeve to said support structure to allow pivoting movement of said other end of said bucket antirollback control rod through the arcuate path defined by the surface of said antirollback control member during raising and lowering of said lift arm means and to allow sliding movement of said bucket antirollback control rod towards said bucket antirollback control member when said lift arm means is raised and said bucket is rolled back and away from said bucket antirollback control member when said lift arm means is lowered and said bucket is rolled forward, and linkage means connecting said bucket antirollback control member to said bucket operating linkage for pivoting said bucket antirollback control member towards said other end of said bucket antirollback control rod in response to movement of said bucket operating lever into its first position and for pivoting said bucket antirollback control member away from said other end in response to movement of said bucket operating lever into its second position, whereby said other end of said bucket antirollback control rod engages the arcuate control surface of said bucket antirollback control member when said bucket is level and said lift arm means is raised to prevent movement of said bucket operating lever into its first position and rollback of said bucket past its level position.
 2. A material-handling device in accordance with claim 1 in which said sleeve terminates short of both ends of said bucket antirollback control rod and said sleeve mounting means includes means for pivotally mounting said sleeve beyond the end thereof whereby the pivoting movement of said bucket antirollback control rod is about a point beyond the end of said sleeve and short of the other end of said bucket antirollback control rod.
 3. A material-handling device comprising in combination a support structure, lift arm means, a bucket, means for pivotally supporting said bucket on one end of the said lift arm means, means for connecting said lift arm means to said support structure, means for operating said bucket to roll said bucket forward and back relative to said lift arm means, a control member, a bucket antirollback link, means for supporting said link between said operating means and said control member for sliding movement of said link towards said control member in response to rollback of said Bucket relative to said lift arm means and for sliding movement away from said control member in response to rolling forward of said bucket relative to said lift arm means, said link having a free end facing said control member, means for connecting said control member to said bucket operating means for moving said control member toward said link in response to rollback of said bucket and for moving said control member away from said link in response to rolling forward of bucket relative to said lift arm means, said control member having a surface positioned to be engaged by the free end of said antirollback link when said bucket is at its level position and said operating means is actuated to roll said bucket back relative to said lift arm means, whereby additional movement of said bucket operating means to roll back the bucket past its level position is prevented.
 4. A material-handling device in accordance with claim 3 in which said bucket operating means includes an operating lever, movable into a first position to roll back said bucket relative to said lift arm means, in which said means connecting said control member to said bucket operating means includes a mechanical linkage interconnecting said control member and said operating lever for movement of said control member towards said link in response to movement of said operating lever into its first position and for movement of said operating lever out of its first position in response to movement of said control member away from said link, whereby engagement of said link with said control member causes movement thereof away from said link to prevent operation of said lever to roll back said bucket past its level position.
 5. A material-handling device in accordance with claim 3 in which said control member includes an arcuate control surface, and in which said link supporting means includes means for allowing pivotal movement of said one end of said link along said arcuate path.
 6. A material-handling device in accordance with claim 3 in which said bucket operating means includes bucket control linkage interconnecting said bucket and said lift arm means, and in which the other end of said link is pivotably connected to said bucket linkage.
 7. A bucket antirollback mechanism for a material-handling device comprising in combination a support structure, lift arm means, means for pivotally supporting one end of said lift arm means on said support structure, means for raising and lowering said lift arm means, a bucket, means for pivotally supporting said bucket on the other end of said lift arm means, bucket control linkage connected between said bucket and said lift arm means, an operating lever, means connecting said operating lever to said bucket control linkage for operating said linkage to roll said bucket back relative to said lift arm means when said operating lever is in a first position and for rolling said bucket forward relative to said lift arm means when said operating lever is in a second position, an antirollback control member, an antirollback control link, means for connecting one end of said link to said bucket control linkage and for supporting the other end of said link for pivotable and sliding movement of said link towards said control member during rollback of said bucket and away from said control member during forward roll of said bucket, said other end of said link being free and facing said control member, and means for connecting said control member to said operating lever for moving said control member towards said control link during movement of said operating lever into its first position and for moving said control member away from said control link during movement of said operating lever into its second position, said control member having a surface positioned to be engaged by the free end of said control link when said operating lever is in said first position and said raising means has raised said lift arm means beyond a predetermined angle, said control member moving away fRom said link in response to the free end of said link engaging said control member when said operating lever is in its first position and said bucket is rolled back to its level position to move said operating lever out of said first position thereby preventing rollback of said bucket past its level position.
 8. A material-handling device comprising in combination lift arm means, a bucket pivotally supported on said lift arm means, means for raising and lowering said lift arm means, means for operating said bucket to roll said bucket forward and back relative to said lift arm means, a control member, a bucket antirollback link, means for supporting one end of said link adjacent to said control member for reciprocable and pivotable movement of said link relative to said control member in response to operation of said bucket and said lift arm means, and means for supporting said control member for movement relative to said one end of said link in response to operation of said bucket operating means whereby engagement of said one end of said link and said control member prevents rollback of said bucket past its level position when said lift arm means is raised in which the reciprocal and pivotable movement of said one end of said link defines an arcuate path, and in which said control member includes an arcuate control surface defined by said path.
 9. A material-handling device in accordance with claim 8 including bucket control linkage interconnecting said bucket and said lift arm means, and means connecting the other end of said link to said linkage for movement of said one end of said link towards said control member during rollback of said bucket and raising of said lift arm means and for moving said one end of said link away from said control member during forward roll of said bucket and lowering of said lift arm means.
 10. A material-handling device in accordance with claim 8 in which said bucket operating means includes a hydraulic cylinder connected between said bucket and said lift arm means and a hydraulic valve for controlling operation of said cylinder to alternatively roll said bucket forward and back, and mechanical linkage means connecting said control member to said valve for moving said control member towards said one end of said link in response to operation of said valve to roll back said bucket and for moving said control member away from said one end of said link in response to operation of said valve to roll said bucket forward, whereby engagement of said link and said control member causes movement of said control member away from said link to close said valve and prevent rollback of the bucket past its level position when said lift arm means are raised. 